Amnesia for childhood sexual abuse is a condition.
The existence of this condition is beyond dispute.
Repression is merely one explanation
– often a confusing and misleading one –
for what causes the condition of amnesia.
Some people sexually abused in childhood
will have periods of amnesia for their abuse,
followed by experiences of delayed recall.http://www.jimhopper.com/memory/

Research on the Effect of Trauma on Memory
Research has shown that traumatized individuals respond by using a variety of psychological mechanisms. One of the most common means of dealing with the pain is to try and push it out of awareness. Some label the phenomenon of the process whereby the mind avoids conscious acknowledgment of traumatic experiences as dissociative amnesia . Others use terms such as repression , dissociative state , traumatic amnesia, psychogenic shock, or motivated forgetting . Semantics aside, there is near-universal scientific acceptance of the fact that the mind is capable of avoiding conscious recall of traumatic experiences. http://www.leadershipcouncil.org/1/tm/tm.html

Recovered memory corroboration rates
"Between 31 and 64 percent of abuse survivors in six major studies reported that they forgot “some of the abuse.” Numbers reporting severe amnesia ranged from under 12% to 59%….Studies report 50-75% of abuse survivors corroborating the facts of their abuse through an outside source."https://ritualabuse.us/research/memory-fms/recovered-memory-corroboration-rates/

Recovered memories have been defined as the phenomenon of partially or fully losing parts of memories of traumatic events, and then later recovering part or all of the memories into conscious awareness. They have also been defined as the recollections of memories that are believed to have been unavailable for a certain period of time[1]. There is very strong scientific evidence that recovered memories exist.[2] This has been shown in many scientific studies. The content of recovered memories have fairly high corroboration rates.

Scientific evidence
There are many studies that have proven that the recovered memories of traumatic events exist. Brown, Scheflin and Hammond found 43 studies that showed recovered memories for traumatic events[3]. The Recovered Memory Project has collected 101 corroborated cases of recovered memories[4]. Hopper's research shows that amnesia for childhood sexual abuse is "beyond dispute." He states that "at least 10% of people sexually abused in childhood will have periods of complete amnesia for their abuse, followed by experiences of delayed recall" [5] In one study of women with previously documented histories of sexual abuse, 38% of the women did not remember the abuse that had happened 17 years before.[6] Most recovered memories either precede therapy or the use of memory recovery techniques[7]. One studied showed that five out of 19 women with histories of familial sexual abuse either forgot specific details or had "blank periods" for these memories[8]. Another study showed that "40% reported a period of forgetting some or all of the abuse"[9]. Herman and Harvey's study showed that 16% of abuse survivors had "complete amnesia followed by delayed recall"[10]. Corwin's individual case study provides evidence of the existence of recovered memories on videotape[11].

Other researchers state:

Research has shown that traumatized individuals respond by using a variety of psychological mechanisms. One of the most common means of dealing with the pain is to try and push it out of awareness. Some label the phenomenon of the process whereby the mind avoids conscious acknowledgment of traumatic experiences as dissociative amnesia. Others use terms such as repression, dissociative state, traumatic amnesia, psychogenic shock, or motivated forgetting. Semantics aside, there is near-universal scientific acceptance of the fact that the mind is capable of avoiding conscious recall of traumatic experiences.[12]

A body of empirical evidence indicates that it is common for abused children to reach adulthood without conscious awareness of the trauma[13]